1. Field of the Invention
The present invention relates to a vehicular lamp with breathing air holes formed in the rear wall of a lamp body, which cooperates with a front lens to define a lamp chamber.
2. Related Art
A conventional vehicular lamp of this type is typically illustrated in FIG. 9. The illustrated one is a vehicular headlamp. As shown, a lamp chamber of the headlamp is defined and hermetically closed by a lamp body 1 and a front lens 2. A reflector 3 with a bulb 4 as a light source, inserted thereinto, is supported by an aiming mechanism (not shown) such that it is tiltable back and forth as well as to the right and left. The aiming mechanism is composed of two aiming screws and one ball joint. Breathing air holes 6a and 6b are formed at positions above and below the bulb 4 set to the rear wall of the lamp body 1, while communicating the inside of the lamp chamber with the outside thereof. The headlamp breathes through the air holes to prevent the dew from being formed on the front lens 2.
When the bulb 4 is turned on, it generates heat. The heat causes air streams by convection (as indicated by arrows A) around the bulb 4. Most of the air streams around the bulb 4 is ascending. As a result, a pressure in the upper portion of the inside of the lamp chamber is higher than in the lower portion. In the upper portion of high pressure air flows out through the air hole 6a, while in the lower portion of low pressure air is introduced thereinto from the outside through the air hole 6b. In this way, air is discharged from the inside of the lamp chamber to the outside, and sucked thereinto from the outside. In other words, the headlamp breaths through the air holes 6a and 6b. This breathing action activates the convection current within the lamp chamber to prevent the formation of the dew condensation.
In the headlamp thus constructed, a gap is present between the reflector 3 and the lamp body 1. Air (heated air), which is left after being discharged through the air hole 6a, flows downward and returns to the front space of the reflector 3, while passing through that gap (as indicated by an arrow B). Therefore, a reduced amount of air circulates between the inside and outside of the lamp chamber, through the air holes 6a and 6b, and hence the convection current A also reduces in its amount and the dew prevention effect.